Batteries used as power sources of electronic equipment have, for example, a cylindrical shape or a prismatic shape. In a cylindrical battery, a metal can deep-drawn to a cylindrical shape (cylindrical drawing) is used, and in a prismatic battery, a metal can deep-drawn to a prismatic shape (prismatic drawing) is used.
On the other hand, in small portable electronic equipment such as a portable information terminal requiring thinness, a relatively thin battery is used. This kind of thin battery is classified into the following types.
(1) A thin battery in which a metal can (deep-drawn can) subjected to the above-mentioned deep-drawing is used, and a metal cover is fitted to an opening of the metal can, followed by welding (e.g., see a conventional prismatic non-aqueous electrolyte secondary battery described in JP 11(1999)-185820 A).
(2) A thin battery using a laminate, in which a metal foil such as an aluminum foil and resin are stacked, as an outer member so as to set the entire thickness small.
(3) A thin battery in which a metal can (shallow-drawn can) subjected to shallow-drawing, such as a lunch box, is used, and a metal cover is fitted to an opening of the metal can, followed by welding (e.g., see a non-aqueous electrolyte solution secondary battery described in JP 11(1999)-185820 A).
In recent years, as seen from the spread of the above-mentioned portable information terminal, there is a strong demand for small and light-weight electronic equipment. Along with this, there also is an increasing demand for thinness of a battery to be mounted on the electronic equipment.
However, a conventional thin battery has a prismatic shape or an elliptically cylindrical shape. Therefore, in order to attach such a battery to equipment or a resin pack (battery pack) to be mounted on the equipment, it is necessary to provide a battery chamber or fix the battery at a predetermined position with a double-faced tape or an adhesive. When the battery chamber is provided, the thickness of the equipment is increased by the thickness of the battery chamber. When the battery is fixed with an adhesive, an increase in thickness of the equipment can be avoided; however, it is difficult to separate the battery for disposal, which is likely to have detrimental effects in modern time as recycling is important.
Furthermore, the conventional thin battery configuration as described in the above (1) to (3) cannot sufficiently meet the demand for further thinness. Alternatively, even if a battery can be made thinner, its strength may not be sufficient, inconvenience is likely to occur in the course of production, it is not easy to set the battery on equipment, etc. Thus, various problems occur.
More specifically, in the battery described in the above (1), a deep-drawn can is used as a battery can, so that there is a predetermined limit to the size to be formed. For example, the thinnest can has a thickness of about 3 mm, and it is impossible or very difficult to obtain a can with a thickness of about 3 mm or less by the current deep-drawing technique. Therefore, in order to obtain such a thin battery can, a stacked material such as a laminate as described above cannot help being used as a battery outer member. In this case, although the thinness of the laminate can be ensured, the strength of the laminate with respect to sticking and bending is smaller than that of a metal can, and furthermore, there is a possibility of swelling of a battery and leakage of liquid.
Furthermore, even if a metal can with a thickness of 3 mm or less can be formed, a deep-drawn can has the following problems.
(A) As the thickness of a metal can is decreased, the width of an opening thereof (opening width in a thickness direction of the can) is decreased, whereby it becomes difficult to insert an electrode in the metal can.
(B) Terminals are attached to attachment holes provided at a metal cover for sealing an opening of a can, via an insulating packing (gasket) made of resin. When the width of the opening becomes narrow, the insulating packing is placed doser to an opening edge. Therefore, when the metal cover is fitted to the opening and bonded thereto by laser welding or the like, the insulating packing is likely to be melted due to welding heat between the metal cover and the can.
(C) For deep-drawing, only an extendable material having a required extensibility is used. Therefore, the kind of metal to be formed is limited, and the hardness of metal to be formed is small. Therefore, a deep-drawn can is weak to the swelling of a battery. Thus, materials that have a large hardness (i.e., that are hard), light weight and strength cannot be used even if desired.
On the other hand, a battery using a shallow-drawn can described in the above (3), more specifically, a battery as described in, for example, JP 11(1999)-185820 A can avoid most of the above-mentioned problems in the battery using a deep-drawn can. However, such a battery also has the following problems.
(a) For example, a peripheral edge of the maximum opening of a can is provided with a cover having the same size as that of the peripheral edge, and the vicinity of the peripheral edge of the maximum opening is welded. Therefore, welding heat is likely to be transmitted to an electrode body (electrode element) in a can and components placed near the welded portion, which may have thermal influence.
(b) In the case where a cover is attached by crimping an outer periphery of the cover and the peripheral edge of an opening (i.e., by seaming), instead of welding, productivity is decreased compared with the case using welding, and there may be a possibility of leakage of liquid from the connected portion between the outer periphery of the cover and the peripheral edge of the opening.
(c) A battery has a simple prismatic shape although it is thin. Therefore, in order to provide a protection circuit required in a secondary battery, it is necessary to separately keep or provide a space for the protection circuit or a base for attachment thereof.
(d) It is necessary to provide a battery chamber for attaching a battery to equipment or a resin pack (battery pack) or to fix a battery at a predetermined position with a double-faced tape or an adhesive. Thus, there are problems similar to those in the case of a prismatic or cylindrical thin battery as described above.